A slide guide apparatus of this type is described in, for example, Japanese Patent Application Laid-Open No. 2003-311495 (which will be hereinafter referred to as patent document 1). In this apparatus, convex spherical portions and concave spherical portions cooperating with the convex spherical portions are provided between a slide and the main body of the press machine, whereby relative tilt between the slide and the main body of the press machine is prevented or absorbed. Thus, surface contact of the sliding surface is ensured, and the surface pressure of the sliding surface is made uniform, whereby abrasion and adhesion caused by heat fusion due to friction can be prevented, and reciprocating motion of the slide can be guided with low friction with a high degree of precision.
More specifically, as shown in FIGS. 1 to 11 of patent document 1, in the slide guide apparatus described in patent document 1, thanks to position adjustment achieved by convex spherical portions of spherical members and concave spherical portions of holders or caps that cooperate with the convex spherical portions, surface contact of flat portions of the spherical members or flat portions of the caps and flat portions of gibs provided on a frame of the press machine that face the flat portions of the spherical members or the flat portions of the caps is always maintained as they slide, whereby up and down motion of the slide is guided. In this slide guide apparatus, the spherical members or the holders are attached to the slide by their flat portions. Thus, complicated spherical surface machining with a high degree of precision on the slide can be eliminated, and machining of the slide is made easy.
Japanese Patent Application Laid-Open No. 2002-11600 (which will be hereinafter referred to as patent document 2) describes a slide guide apparatus in which a slide of a press machine is provided with spherical blocks or cylindrical blocks each having an L-shaped guide surface (constituted by surfaces arranged in an L-shape) for receiving a part of the frame of the press machine, and sliding of the aforementioned L-shaped guide surfaces and guide surfaces provided on the frame of the press machine is enabled with surface contact being always maintained by the effect of the spherical surface of the spherical blocks or the cylindrical surfaces of the cylindrical blocks.
Japanese Patent Application Laid-Open No. 2002-59298 (which will be hereinafter referred to as patent document 3) also discloses a slide guide apparatus in which slide gibs are provided on a slide. The slide gib has an L-shaped sliding surface that slides on a guide surface of a fixed gib provided on a column and a cylindrical portion that is inserted along the front-rear direction of the slide and rotatable relative to the slide to enable a sliding surface of the slide gib and a sliding surface of the fixed gib to slide with surface contact being always maintained.
The apparatus described in patent document 1 can prevent partial contact of sliding surfaces of a guide surface (e.g. a flat portion of the spherical member) on the slide of the slide guide apparatus and a guide surface extending along the sliding direction on a gib on the frame to achieve uniform contact over the entire sliding surfaces.
However, if the surface pressure of the sliding surfaces is required to be made small even when a relatively heavy eccentric load acts on the slide to generate a strong rotational force, the contact area of the guide surface (i.e. the flat portion of the spherical member) on the slide and the guide surface extending on the gib on the frame needs to be made large. However, enlargement of the contact area (or sliding area) of the guide surface (i.e. the flat portion of the spherical member) on the slide necessitates enlargement of the diameter of the spherical member having a spherical shape, which may possibly lead to restriction of mounting space of the spherical member on the slide or other problems. In addition, enlargement of the diameter of the spherical member requires enlargement of the width of the guide surface extending on the gib on the frame. As a result, the slide guide apparatus as a whole will require a large space.
On the other hand, in a case where the flat portion of the cap constitutes the guide surface that is in contact with and slides on the guide surface on the gib on the frame, the flat portion may be configured to have a rectangular shape that is elongated in the sliding direction in order to enlarge the contact area. However, in this case also, the pressure-receiving surface on the back side of the flat portion of the cap is spherical, and therefore, on the back side of the rectangular flat portion (or sliding surface) of the cap are a portion in which the spherical pressure receiving surface that engages with the spherical member is present and a portion in which the spherical pressure receiving surface is not present (i.e. a portion away from the spherical pressure receiving surface) along the sliding direction. Thus, the portion in which the pressure receiving surface is not present on the back side has a lower rigidity than the portion in which the spherical pressure receiving surface is present and deforms more easily by a load. Therefore, the surface pressure of the portion of the sliding surface in which the pressure receiving surface is not present on the back side will become lower.
For the above reason, even in a case where the flat portion of the cap has a rectangular shape, if the force acting on the slide guide is strong, the force cannot be distributed uniformly over the entire guide surface (or sliding surface), but the surface pressure in the portion in which the pressure receiving surface that engages with the spherical member present becomes high. Therefore, even when the guide surface of the cap is configured to have a rectangular shape elongated in the sliding direction, a great effect cannot be expected.
In the apparatuses described in patent documents 2 and 3, a plurality of intersecting guide surfaces are provided on the frame, and a cylindrical block (or slide gib) having a plurality of guide surfaces (having, for example, an L-shape) cooperating with the guide surfaces on the frame is fitted in the slide. This apparatus is intended to always maintain surface contact of a guide surface on the frame and a guide surface of a cylindrical block (or slide gib) fitted in the slide without partial contact as they slide, by virtue of the operation of the cylindrical surface of the cylindrical block (or slide gib) (i.e. rotation along the cylindrical surface or rotation about the center of the cylinder). However, even in a case where the guide surfaces (having, for example, an L-shape) provided on the cylindrical block (or slide gib) are flat surfaces parallel to the center of the cylindrical surface, rotation of the cylindrical block (or slide gib) along the cylindrical surface is not contributive to surface contact of the guide surfaces, unless the guide surfaces on the frame are flat surfaces parallel to the cylinder center of the cylindrical block (or slide gib). Therefore, there is a possibility that a significant degree of partial contact occurs depending on the situation, for example in a case where the load acting on the slide is heavy and/or eccentric.
In order to achieve surface contact of the guide surfaces (having, for example, an L-shape) on the cylindrical block (or slide gib) and the respective corresponding guide surfaces on the frame, it is necessary that the angle formed by the guide surfaces (having, for example, an L-shape) on the cylindrical block (or slide gib) and the angle formed by the corresponding guide surfaces on the frame be made equal to each other. However, neither the cylindrical block (or slide gib) nor the frame is provided with means for adjusting the angle of their guide surfaces, and therefore the degree of accuracy of the angle formed by the guide surfaces depends on the degree of precision in machining and assembling during manufacturing of the cylindrical block (or slide gib) and the frame.
Since there is a limit to the degree of precision in machining and assembling, it is difficult, as a matter of fact, to manufacture a slide guide apparatus in such a way that it can achieve simultaneous surface contact of the guide surfaces intersecting at a certain angle with an uniform surface pressure.
Even when the guide surfaces of the cylindrical block (or slide gib) intersecting at a predetermined angle are in surface contact with the respective corresponding guide surfaces on the frame, if a large moment acts on the slide due to an eccentric press load, the guide surfaces (which are arranged to form a predetermined angle) of the cylindrical block (or slide gib) that receives the moment will be pressed against the guide surfaces on the frame, whereby the predetermined angle formed by the intersecting guide surfaces may be enlarged. Thus, there is a possibility that uniformity in the surface pressure cannot be maintained.